1. Field of the Invention
The present invention relates to medical procedures in which an invasive device is inserted into a living body, and more particularly concerns the tracking of such a device with the use of radiofrequency fields.
2. Description of Related Art
X-ray fluoroscopes are used routinely to monitor the placement of invasive devices during diagnostic and therapeutic medical procedures. Conventional X-ray fluoroscopes are designed to minimize X-ray dosage. Nevertheless, some procedures can be very long and the accumulated X-ray dose to the patient can become significant. The long term exposure of the attending medical staff is of even greater concern since they participate in these procedures regularly. Consequently, it is desirable to reduce the X-ray dose during these procedures.
Methods to track an end of an invasive device without the use of X-rays have been disclosed previously in the aforementioned patent applications Ser. Nos. 07/753,563 and 07/753,565, both filed Sep. 3, 1991 hereby incorporated by reference. These applications describe systems in which an invasive device incorporating a radiofrequency coil is placed within the body and its position is followed by broadcasting and detecting a radiofrequency (RF) signal.
Typically a connection between an invasive device and the remainder of a tracking system is made by standard physical connections (e.g. BNC or SMD connectors). Invasive devices such as RF catheters and biopsy needles can be constructed with conventional connectors only if such connector is attached to a invasive device exiting the side of the device, since the interior of the device must be available to provide access for guide wires, contrast media and/or any other object which is part of the procedure. A guide wire, on the other hand, is placed within the body prior to the insertion of a catheter. Since the catheter is placed over the exposed end of the guide wire and since it might need to be changed during the procedure, the guide wire must have a connection whose cross-section is smaller than the catheter. One way to avoid this problem is to make the guide wire very long and place the catheter over the guide wire before it is inserted into the patient. Very long guide wires, however, would be cumbersome to use, and changing the catheter with such a system would necessitate the removal of both the guide wire and catheter.
Another important consideration is the maintenance of a sterile instrument and work area during the procedure. In a typical X-ray angiography procedure, the doctor removes the guide wire every few minutes to sterilize it and to remove any thrombus which might have collected. An exceedingly long catheter or guide wire, or one-which is difficult to connect and disconnect, would increase the risk of contamination. The sterility of the equipment to which the catheter and guide wire are attached is also important. Any physical contact of the catheter or guide wire with a non-sterile device requires that the device be either re-sterilized or discarded.